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Abstract:

Disclosed herein is a process for recycling water in a cellulosic
conversion process that comprises selecting process stream(s) that may
contain reduced levels of inhibitors and subsequently subjecting the
stream(s) to a treatment process to produce treated water. The treated
water is thereafter recycled to the cellulosic conversion process,
associated utilities or the seal water system. The process streams
selected for treatment may comprise less than 5 wt % organic content
and/or less than 5 wt % inorganic content. The process of the invention
comprises at segregating process streams based on their treatment
requirements. The segregated process streams may be sent to respective
separate treatments selected from anaerobic digestion, aerobic digestion,
physical separation and chemical treatment.

Claims:

1. A cellulosic conversion process employing water recycle, the process
comprising the steps of: (i) pretreating a lignocellulosic feedstock to
produce a pretreated feedstock; (ii) hydrolyzing cellulose in the
pretreated feedstock with cellulase enzymes to produce glucose; (iii)
fermenting at least the glucose with microorganisms to produce a
fermentation broth comprising alcohol; (iv) distilling the fermentation
broth to produce concentrated alcohol and still bottoms; (v) obtaining
two or more of the following process streams from the cellulosic
conversion process, associated utilities or seal water system: (a) spent
cleaning solution used to clean process equipment utilized during any of
the preceding steps (i) to (iv); (b) a process condensate stream obtained
during said cellulosic conversion process; (c) a rectifier effluent
stream obtained from the step of distilling the fermentation broth; (d) a
blowdown stream obtained from a cooling tower or boiler system; (e) a
regenerated stream; and (f) spent seal water obtained from one or more
pieces of equipment used during any of the preceding steps (i) to (iv);
(vi) conducting a treatment process comprising subjecting one or more of
said process streams to an anaerobic digestion and one or more of said
process streams to an aerobic digestion, said treatment process resulting
in one or more treated water streams; and (vii) re-circulating the one or
more treated water streams resulting from the treatment process to the
cellulosic conversion process, associated utilities, seal water system or
a combination thereof.

2. The process of claim 1, wherein said one or more treated water streams
that are re-circulated comprise either an effluent stream from the
anaerobic digestion, an effluent stream from aerobic digestion, both
effluent streams, or one or more streams derived therefrom.

3. The process of claim 1, further comprising feeding an effluent stream
from the anaerobic digestion to the aerobic digestion.

4. The process of claim 3, further comprising obtaining a second effluent
stream from the anaerobic digestion and feeding said second effluent
stream to a physical separation, a chemical separation or discharging
said second effluent stream from the process.

5. The process of claim 3, wherein the one or more treated water streams
that are re-circulated comprise an effluent stream from the aerobic
digestion, or one or more streams derived therefrom; and wherein the
treatment process further comprises the use of a second aerobic
digestion, wherein an effluent stream from said second aerobic digestion,
or one or more streams derived therefrom, is discharged from the process.

6. The process of claim 2, wherein the effluent stream from the anaerobic
or aerobic digestion, or both effluent streams, are further treated by
one or more of reverse osmosis, ion exchange and filtration to remove
sediment, ions or both sediment and ions prior to the step of
re-circulating.

7. The process of claim 1, wherein the treatment process further
comprises subjecting the blowdown stream, the regenerated stream, the
spent seal water stream, or a combination thereof, to a reverse osmosis
or ion exchange operation.

8. The process of claim 1, wherein the two or more process streams
obtained from step (v) comprise at least the process condensate stream.

9. The process of claim 1, wherein the treatment process reduces the
concentration of acetic acid relative to the feed.

10. The process of claim 1, wherein step v comprises combining two or
more of the process streams.

11. The process of claim 1, wherein the condensate stream is a flash
condensate stream resulting from a step of flashing conducted on the
pretreated feedstock to reduce the temperature of same.

12. The process of claim 1, wherein the condensate stream is an
evaporator condensate stream resulting from a step of evaporating the
still bottoms in an evaporator unit and condensing vapour obtained
therefrom.

13. The process of claim 1, wherein the one or more treated water streams
are re-circulated to the step of pretreating, hydrolyzing, fermenting, a
cleaning system, a residue processing stage, or a combination thereof.

14. The process of claim 1, wherein the one or more treated water streams
are re-circulated to the cooling tower system, boiler feed water system,
or any combination thereof.

15. A process for recycling water in a cellulosic conversion process that
produces an alcohol, the process comprising the steps of: (i) pretreating
a lignocellulosic feedstock to produce a pretreated lignocellulosic
feedstock; (ii) hydrolyzing cellulose in the pretreated feedstock with
cellulase enzymes to produce glucose; (iii) fermenting at least the
glucose with microorganisms to produce a fermentation broth comprising
the alcohol; (iv) distilling the fermentation broth to produce
concentrated alcohol and still bottoms; (v) obtaining two or more of the
following process streams for further treatment and recycle, wherein the
process streams arise from the cellulosic conversion process, associated
utilities or a seal water system: (a) spent cleaning solution used to
clean process equipment utilized during any of the preceding steps (i) to
(iv); (b) a process condensate stream obtained during said cellulosic
conversion process; (c) a rectifier effluent stream obtained from the
step of distilling the fermentation broth; (d) a blowdown stream obtained
from a cooling tower or boiler system; (e) a regenerated stream; and (f)
spent seal water obtained from one or more pieces of equipment used
during any of the preceding steps (i) to (iv); (vi) subjecting two or
more of said process streams to a treatment process, thereby producing
one or more treated water streams, said treatment process comprising:
feeding two or more of the process streams to respective separate
treatments selected from anaerobic digestion, aerobic digestion, physical
separation and chemical treatment; and (vii) re-circulating the one or
more treated water streams to the cellulosic conversion process,
associated utilities, seal water system or a combination thereof.

16. The process of claim 15, wherein, during the treatment process, three
process streams are fed to respective separate treatments.

17. The process of claim 15, wherein one of said process streams is
discharged to the environment.

18. The process of claim 16, wherein one or more of the process streams
are subjected to anaerobic digestion and one or more of the process
streams are subjected to aerobic digestion.

19. The process of claim 18, wherein one or more of the process streams
are subjected to reverse osmosis, ion exchange or a combination thereof.

20. The process of claim 18, wherein the one or more process streams
subjected to aerobic digestion are process streams selected from the
spent cleaning solution, the process condensate stream, the rectifier
effluent and the spent seal water.

21. The process of claim 15, wherein the two or more process streams sent
to the respective separate treatments each result from combining two or
more of the process streams of step (v).

22. A process for recycling water in a cellulosic conversion process that
produces a fermentation product, the process comprising the steps of: (i)
obtaining process streams for further treatment and recycle, wherein the
process streams arise from the cellulosic conversion process, associated
utilities or a seal water system; (ii) subjecting said process streams to
a treatment process, thereby producing one or more treated water streams,
said treatment process comprising: at least a step of feeding two or more
of the process streams to respective separate treatments selected from
anaerobic digestion, aerobic digestion, physical separation and chemical
treatment, wherein the process streams comprise less than 5 wt % organic
content and less than 5 wt % inorganic content; and (iii) re-circulating
the one or more treated water streams to the cellulosic conversion
process, associated utilities, seal water system or a combination
thereof.

23. The process of claim 22, wherein one or more of the process streams,
or one or more streams derived therefrom, are fed to aerobic digestion.

24. The process of claim 23, wherein the one or more process streams fed
to aerobic digestion are spent cleaning solution, a process condensate
stream, a rectifier effluent, spent seal water and a combination thereof.

Description:

TECHNICAL FIELD

[0001] The present invention relates to an improved process for reducing
water requirements in a cellulosic conversion process.

BACKGROUND OF THE INVENTION

[0002] Lignocellulosic feedstock is a term commonly used to describe
plant-derived biomass comprising cellulose, hemicellulose and lignin.
Much attention and effort has been applied in recent years to the
production of fuels and chemicals, primarily ethanol, from
lignocellulosic feedstocks, such as agricultural wastes and forestry
wastes, due to their low cost and wide availability.

[0003] The first chemical processing step for converting lignocellulosic
feedstock to ethanol, or other fermentation products, involves breaking
down the fibrous lignocellulosic material to liberate sugar monomers from
the feedstock for conversion to a fermentation product in a subsequent
step of fermentation.

[0004] There are various known methods for producing fermentable sugars
from lignocellulosic feedstocks, the most prominent involving an acid or
alkali pretreatment followed by hydrolysis of cellulose with cellulase
enzymes and β-glucosidase. The purpose of the pretreatment is to
increase the cellulose surface area, with limited conversion of the
cellulose to glucose. Acid pretreatment typically hydrolyses the
hemicellulose component of the feedstock to yield xylose, glucose,
galactose, mannose and arabinose and this is thought to improve the
accessibility of the cellulose to cellulase enzymes. The cellulase
enzymes hydrolyse cellulose to cellobiose which is then hydrolysed to
glucose by β-glucosidase.

[0005] After production of a stream comprising fermentable sugar from the
lignocellulosic feedstock, the sugars are fermented to ethanol or other
fermentation products. If glucose is the predominant substrate present,
the fermentation is typically carried out with a yeast that converts this
sugar and other hexose sugars present to ethanol, although bacteria are
also known for such purpose. This conversion can be carried out by a
variety of organisms, including Saccharomyces spp. The ethanol is
recovered from the fermentation broth, or "beer", by distillation. A
still bottoms stream comprising dissolved residual organic and inorganic
components as well as suspended lignin solids remains after distillation.

[0006] Utilizing lignocellulosic feedstocks for ethanol production offers
an attractive alternative to burning or land-filling them, which is a
practice commonly employed in the agriculture sector. Another advantage
of these feedstocks is that the lignin byproduct, which remains after the
cellulose conversion process, can be used as a fuel to power the process
instead of fossil fuels. Several studies have concluded that, when the
entire production and consumption cycle is taken into account, the
production of ethanol from lignocellulosic feedstocks generates close to
zero greenhouse gases.

[0007] However, despite the foregoing advantages, there are still hurdles
to be overcome in order to make cellulosic ethanol conversion processes
more sustainable. Cellulosic ethanol facilities should be built at large
scale to be economically viable, but this requires large amounts of
feedstock and consequently large amounts of water. When fresh water
requirements for the process are high, it is necessary for the plant to
be located near a water source, which in turn reduces the options
available for plant site selection. Moreover, treatment of the incoming
water and handling and disposal of water effluent from the plant is
costly. Zero liquid discharge to the environment would be highly
desirable.

[0008] Water recycle has been suggested as a means to both reduce fresh
water requirements and the amount of wastewater that must be disposed of.
However, water recycle has its own set of shortcomings that must be
addressed to make it economically feasible.

[0009] For instance, recycling streams can increase the levels and/or the
nature of the inhibitors in the process, thereby negatively impacting the
ethanol production process. The pretreated streams generated during an
acidic or basic lignocellulosic pretreatment process contain a number of
compounds that are inhibitory to the enzymes used for enzymatic
hydrolysis and the microorganisms used for ethanol fermentation
(collectively referred to herein as "biocatalysts"). These inhibitory
compounds may be inorganic or organic, suspended or dissolved, identified
or unidentified and may have additive or synergistic impacts on the
biocatalysts. Even if the biocatalysts have been acclimatized to the
inhibitors present in process streams, further increases in the
concentration of these inhibitors, or the introduction of different
inhibitors to process streams containing pre-existing inhibitors, may
increase the overall stress on the biocatalysts to the point that their
performance is severely impacted.

[0010] One potent class of inhibitors generated during cellulosic ethanol
conversion processes is phenolic compounds. When plant biomass is
pretreated in a cellulosic ethanol process prior to enzymatic hydrolysis,
simple or oligomeric phenolics and derivatives can be generated from
lignin modification and/or degradation. These compounds are a known
inhibitor for biomass-converting enzymes. Examples of phenolic compounds
which have been demonstrated to be inhibitory to cellulose-degrading
enzymes include vanillin, syringaldehyde, trans-cinnamic acid and
hydroxybenzoic acid, as well as phenolic hydroxyl groups associated with
lignin itself (Enzyme and Microbial Technology, Vol 46, Issues 3-4, pages
170-176; Journal of Biobased Materials and Bioenergy, Vol 2, No 1, pages
25-32). As these compounds inhibit the enzymes even at very low
concentrations, any increase in the concentration, such as through
recycle of streams containing these compounds in the process, would
further impact the performance of the enzymes.

[0011] Another particularly potent inhibitor in cellulosic ethanol
conversion processes is acetic acid, which is produced by the release of
acetyl groups present on lignocellulosic feedstocks during chemical
pretreatment. In particular, acetic acid is a known inhibitor of
fermenting microorganisms employed to ferment glucose to ethanol. The
microorganism is already inhibited by the natural levels of the acetic
acid in the fermentation process, and any further increase in its levels,
such as would be the case if streams which contain acetic acid were
recycled in the process, would further impact the performance of the
microorganism. Other potential inhibitors of biocatalysts generated
during pretreatment include inorganic salts, hydroxymethylfurfural (HMF)
and furfural.

[0012] Acetic acid poses an even larger challenge for cellulosic ethanol
processes relative to conventional first generation ethanol processes
(i.e., ethanol produced from corn not lignocellulosic feedstock), as the
levels present in the streams are much higher. Kellsall and Lyons ("The
Alcohol Textbook", Ed. K. Jaeques, T. P. Lyons and D. R. Kelsall, 1999,
Nottingham University Press, Nottingham, United Kingdom, incorporated
herein by reference) note that typical levels of acetic acid in a
conventional corn ethanol fermentation range between 0.014 and 0.02 wt %.
They further note that acetic acid can be produced by contaminants, and
that levels at or above 0.05 wt % are known to be inhibitory to yeast. By
contrast, in a cellulosic ethanol process, depending on the pretreatment
conditions and the composition of the feedstock, acetic acid levels in
the feed stream to fermentation can range from 0.1-1.2 wt %, which is
between 6 and 70 times more concentrated than corn ethanol processes and
above known inhibition levels. Cellulosic conversion processes are also
susceptible to bacterial contamination, which can add more acetic acid
due to production by the contaminating bacteria. With acetic acid levels
already well above typical levels, any further acetic acid added through
a recycle process would be detrimental to the process, and would require
additional processing to manage, which would impact the economic
viability of the process.

[0013] Washing steps after pretreatment can help reduce the levels of
acetic acid, however adding more water to the process can impact the
economics of the process, as the added water must later be removed.
Another method that has been proposed to reduce the concentration of
inhibitors is a process known as overliming, which involves the addition
of lime to precipitate the inhibitors. However, the addition of lime
produces gypsum, which is costly to dispose of, results in scale
deposition, requires additional water usage and reduces sugar yield.

[0014] Anaerobic fermentation of still bottoms remaining after
distillation, followed by re-circulation of effluent to the process is
one of many potential options the inventors have identified for treating
and recycling streams in cellulosic ethanol processes and can be a
cost-effective option. However, anaerobic treatment systems are sensitive
to the presence of high sulfate levels. In cellulosic conversion
processes employing sulfuric acid pretreatment, sulfate salts are
generated during adjustment of the pretreated feedstock with alkali.
Alternatively, alkali pretreated feedstock can be treated with sulfuric
acid prior to enzymatic hydrolysis, which also generates sulfate salts.
Regardless of their source, if sulfate-rich streams are sent to anaerobic
digesters prior to their recycle, complicated process steps are required
to remove these salts prior to anaerobic treatment, which, in turn, can
increase both the capital and operating costs of the process.

[0015] Thus, there is a need in the art for an improved process of water
recycle in a cellulosic conversion process that reduces the build-up of
inhibitors, while reducing capital and operating costs.

SUMMARY OF THE INVENTION

[0016] It is an object of the invention to reduce water requirements in a
cellulosic conversion process.

[0017] Disclosed herein is a cellulosic conversion process employing water
recycle that comprises obtaining process streams generated during the
process that contain lower levels of inhibitors and/or other deleterious
components relative to other process streams, and subsequently subjecting
the process streams to a treatment process. The treatment process
comprises feeding two or more process streams to separate respective
treatments, wherein the particular stream(s) fed to each treatment is
selected based on its specific treatment requirement, which in turn
depends on the organic and inorganic components present in the stream(s).
The resultant treated water stream or streams are thereafter recycled to
the cellulosic conversion process, associated utilities, the seal water
system or a combination thereof.

[0018] The two or more process streams subjected to the treatment process
include spent cleaning solution used to clean process equipment utilized
during the cellulosic conversion process; a process condensate stream
obtained during the cellulosic conversion process; rectifier effluent
from a distillation; a blowdown stream obtained from a cooling tower or
boiler system; a regenerated stream; and spent seal water obtained from
one or more pieces of equipment used during the cellulosic conversion
process.

[0019] The processes disclosed herein have numerous benefits over
conventional cellulosic conversion processes involving water recycle.
Advantageously, by selecting the above process streams from the
cellulosic conversion process for recycle that contain lower levels of
inhibitors or other undesirable components and by segregating those
process streams with similar treatment requirements, the overall
treatment system requirements can be minimized. Stream segregation
reduces the size of the treatment equipment only to what is necessary to
provide treated water streams for recycle having inhibitor concentrations
reduced to a level that does not have a significant impact on
bio-catalyst (e.g., yeast and enzyme) performance. Thus, the invention
allows the capital and operating costs of the process to be reduced,
while maintaining the level of treatment of the process stream(s) that is
required to meet recycle requirements of the process. The cellulosic
conversion process may comprise the steps of pretreating a
lignocellulosic feedstock, hydrolyzing cellulose in the pretreated
feedstock to produce glucose, fermenting at least the glucose to produce
a fermentation broth comprising an alcohol and distilling the alcohol to
produce concentrated ethanol and still bottoms. Preferably, the alcohol
is ethanol.

[0020] In one embodiment of the invention, the two or more process streams
comprise at least a process condensate stream. The process condensate
stream may be flash condensate or evaporator condensate. The flash
condensate may result from a step of flashing conducted on the pretreated
feedstock to decrease the temperature of same. The evaporated condensate
may result from evaporating still bottoms in an evaporator unit and
condensing vapour obtained therefrom. The step of obtaining the process
stream may comprise combining two or more of the process streams.

[0021] In one aspect of the invention, the treatment process comprises at
least a step of feeding one or more of the process streams to an
anaerobic digestion and one or more of the process streams to an aerobic
digestion. One or more treated water streams resulting from the treatment
process are re-circulated to the cellulosic conversion process,
associated utilities, seal water system or a combination thereof. The
treated water stream(s) resulting from the treatment process may comprise
either an effluent stream from the anaerobic digestion, an effluent
stream from the aerobic digestion, both effluent streams, or one or more
streams derived therefrom. The effluent stream from the anaerobic or
aerobic digestion, or both effluent streams, may be further treated by
one or more of reverse osmosis and filtration to remove sediment prior to
the step of re-circulating.

[0022] In further embodiments, an effluent stream from the anaerobic
digestion is fed to the aerobic digestion. A second effluent stream from
the anaerobic digestion may be fed to a physical separation, a chemical
separation or discharged from the process. The treated water stream(s)
that is re-circulated may comprise an effluent stream from the aerobic
digestion. The treatment may comprise the use of a second aerobic
digestion, wherein an effluent stream from the second aerobic digestion,
or one or more streams derived therefrom, is discharged from the process.
The effluent stream from the anaerobic or aerobic digestion, or both
effluent streams, may be further treated by one or more of reverse
osmosis, ion exchange and filtration to remove sediment, ions or both
sediment and ions prior to the step of re-circulating. The treatment
process may further comprise subjecting the blowdown stream, the
regenerated stream, the spent seal water stream, or a combination
thereof, to a reverse osmosis or ion exchange operation.

[0023] In some embodiments of the invention, the treatment process reduces
the concentration of acetic acid relative to the feed.

[0024] The treated water stream may be re-circulated to a cooling tower
system, boiler feed water system, the seal water system, or any
combination thereof. In further embodiments of the invention, the one or
more treated water streams are re-circulated to the step of pretreating,
hydrolyzing, fermenting, to a cleaning system, to residue processing
stage or a combination thereof.

[0025] According to a further aspect of the present invention, the
treatment process comprises feeding two or more process streams from the
cellulosic conversion process to respective separate treatments selected
from anaerobic digestion, aerobic digestion, physical separation and
chemical treatment. The two or more process streams subjected to the
treatment process are selected from spent cleaning solution used to clean
process equipment utilized during the cellulosic conversion process; a
process condensate stream obtained during the cellulosic conversion
process; rectifier effluent from a distillation; a blowdown stream
obtained from a cooling tower or boiler system; a regenerated stream; and
spent seal water obtained from one or more pieces of equipment used
during the cellulosic conversion process. One or more treated water
streams resulting from the treatment process are then re-circulated to
the cellulosic conversion process, associated utilities or seal water
system. The two or more process streams sent to the separate treatments
may each result from combining two or more of the aforesaid process
streams.

[0026] According to one embodiment of this aspect of the invention, during
the treatment process, three process streams are fed to respective
separate treatments in the treatment process. According to a further
embodiment of the invention, one of the process streams is discharged to
the environment.

[0027] In certain embodiments of this aspect of the invention, some
streams may be fed to an anaerobic digester and others fed to an aerobic
digester. One or more treated streams obtained from either or both of the
anaerobic and aerobic digestions are then re-circulated to the cellulosic
conversion process, associated utilities or the seal water system. Prior
to re-circulation, the foregoing treated streams may be treated further
by aerobic digestion and/or a physical or chemical separation step, such
as reverse osmosis, ion exchange or filtration.

[0028] In yet further embodiments of the invention, process streams from
the cellulosic conversion process are fed to an anaerobic digestion,
others are fed to an aerobic digestion, while others are fed to a
chemical treatment step such reverse osmosis and/or ion exchange. Treated
streams obtained from either or all of these treatment steps within the
treatment process are then re-circulated to the cellulosic conversion
process, associated utilities, the seal water system or a combination
thereof. Prior to re-circulation, the foregoing treated streams may be
treated further by aerobic digestion and/or a physical or chemical
separation step, such as reverse osmosis, ion exchange or filtration.

[0029] According to a further aspect of the invention, there is provided a
process for recycling water in a cellulosic conversion process that
produces a fermentation product, the process comprising the steps of: (i)
obtaining process streams for further treatment and recycle, wherein the
process streams arise from the cellulosic conversion process, associated
utilities or a seal water system; (ii) subjecting the process streams to
a treatment process, thereby producing one or more treated water streams,
the treatment process comprising: at least a step of feeding two or more
of the process streams to respective separate treatments selected from
anaerobic digestion, aerobic digestion, physical separation and chemical
treatment, wherein the process streams comprise less than 5 wt % organic
content and less than 5 wt % inorganic content; and (iii) re-circulating
the one or more treated water streams to the cellulosic conversion
process, associated utilities, seal water system or a combination
thereof.

[0030] In one embodiment of the invention, one or more process streams, or
one or more streams derived therefrom, are fed to aerobic digestion.
Preferably, the one or more streams fed to aerobic digestion are spent
cleaning solution, a process condensate stream, a rectifier effluent,
spent seal water and a combination thereof.

BRIEF DESCRIPTION OF THE FIGURES

[0031]FIG. 1 depicts process streams that may be selected for treatment
and recycle in a cellulosic conversion process to produce alcohol. The
streams may be obtained from the conversion process itself, from the
associated utilities and/or the seal water system.

[0032]FIG. 2 depicts a treatment process in which process streams from a
cellulosic conversion process, associated utilities and/or a seal water
system are treated using anaerobic digestion, followed by optional steps
of aerobic digestion and physical separation, to produce a treated water
stream that is recycled.

[0033]FIG. 3A depicts a treatment process in which some process streams
from a cellulosic conversion process, associated utilities and/or a seal
water system are treated using anaerobic digestion, while others are
treated by aerobic digestion, followed by an optional step of physical
separation, to produce a treated water stream that is recycled.

[0034]FIG. 3B is similar to FIG. 3A, except in FIG. 3A one aerobic
digestion is employed, while in FIG. 3B, two aerobic digestion steps are
employed.

[0035]FIG. 4 depicts a treatment process in which some process streams
from a cellulosic conversion process, associated utilities and/or a seal
water system are treated using anaerobic digestion, others are treated by
aerobic digestion, while others are treated using reverse osmosis,
followed by an optional step of physical separation, to produce a treated
water stream that is recycled.

DETAILED DESCRIPTION OF THE INVENTION

[0036] The following description is of a preferred embodiment by way of
example only and without limitation to the combination of features
necessary for carrying the invention into effect. The headings provided
are not meant to be limiting of the various embodiments of the invention.
Terms such as "comprises", "comprising", "comprise", "includes",
"including" and "include" are not meant to be limiting. In addition, the
use of the singular includes the plural, and "or" means "and/or" unless
otherwise stated. Unless otherwise defined herein, all technical and
scientific terms used herein have the same meaning as commonly understood
by one of ordinary skill in the art.

Description of Feedstock Types

[0037] By the term "cellulosic conversion process", it is meant a process
for producing a fermentation product from a lignocellulosic feedstock,
including, but not limited to, ethanol.

[0038] By the term "lignocellulosic feedstock", it is meant any type of
plant biomass such as, but not limited to, non-woody plant biomass,
cultivated crops such as, but not limited to grasses, for example, but
not limited to, C4 grasses, such as switch grass, cord grass, rye grass,
miscanthus, reed canary grass, or a combination thereof, sugar processing
residues, for example, but not limited to, bagasse, such as sugar cane
bagasse, beet pulp, or a combination thereof, residues remaining after
grain processing, such as, but not limited to corn fiber, corn cobs after
kernel removal, corn stover, or a combination thereof, agricultural
residues, for example, but not limited to, soybean stover, corn stover,
rice straw, sugar cane straw, rice hulls, barley straw, corn cobs, wheat
straw, canola straw, oat straw, oat hulls, corn fiber, or a combination
thereof, forestry biomass for example, but not limited to, recycled wood
pulp fiber, sawdust, hardwood, for example aspen wood, softwood, or a
combination thereof. Furthermore, the lignocellulosic feedstock may
comprise lignocellulosic waste material or forestry waste materials such
as, but not limited to, newsprint, cardboard and the like.
Lignocellulosic feedstock may comprise one species of fiber or,
alternatively, lignocellulosic feedstock may comprise a mixture of fibers
that originate from different lignocellulosic feedstocks. In addition,
the lignocellulosic feedstock may comprise fresh lignocellulosic
feedstock, partially dried lignocellulosic feedstock, fully dried
lignocellulosic feedstock, or a combination thereof. Moreover, new
lignocellulosic feedstock varieties may be produced from any of those
listed above by plant breeding or by genetic engineering.

[0039] Lignocellulosic feedstocks comprise cellulose in an amount greater
than about 20%, more preferably greater than about 30%, more preferably
greater than about 40% (w/w). For example, the lignocellulosic material
may comprise from about 20% to about 50% (w/w) cellulose, or any amount
therebetween. Furthermore, the lignocellulosic feedstock comprises lignin
in an amount greater than about 10%, more typically in an amount greater
than about 15% (w/w). The lignocellulosic feedstock may also comprise
small amounts of sucrose, fructose and starch.

Feedstock Size Reduction

[0040] The lignocellulosic feedstock is generally first subjected to size
reduction by methods including, but not limited to, milling, grinding,
agitation, shredding, compression/expansion, or other types of mechanical
action. According to the invention, the lignocellulosic feedstock from
the size reduction process produces a size-reduced feedstock comprising
particles of a defined length. At least 90% by weight of the particles in
the size reduced feedstock may have a length less than between about 1/8
and about 6 inches. As would be appreciated by those of ordinary skill in
the art, lignocellulosic feedstock that has been subjected to size
reduction comprises feedstock particles having a range of sizes and
shapes.

[0041] Size reduction by mechanical action can be performed by any type of
equipment adapted for the purpose, for example, but not limited to,
hammer mills, tub-grinders, roll presses, refiners, shredders and
hydrapulpers. It should be appreciated that the lignocellulosic feedstock
need not be subjected to size reduction if the particle size of the
feedstock is already between 1/2 to 6 inches.

[0042] If size reduction is required, it can be performed while the
lignocellulosic feedstock is dry or moist, i.e., having a moisture
content of 0% to about 20%, or while water is added to the
lignocellulosic feedstock. Dry shredding can be carried out, for example,
with an SSI or Grizzly grinder, hammer mill or tub grinder, while wet
shredding may be performed with pulpers. When dry shredding is employed,
the particle size may be between about 1/2 to about 6 inches. When hammer
milling, the particle size may be less than about 4 inches to less than
about 1/2 inch depending on the size of the screens used in the hammer
mill.

[0043] The size of the lignocellulosic feedstock particles can have an
impact on both processing of the feedstock and in the chemical reactions
involved during pretreatment. A person of ordinary skill in the art could
select a concentration of feedstock particles and particle
characteristics that allows for ease of processing and that achieves a
desired reactivity of the feedstock in pretreatment.

[0044] For the purposes of this specification, the size of the feedstock
particles is determined by image analysis using techniques known to those
of ordinary skill in the art. An example of a suitable image analysis
technique is disclosed in Igathinathane (Sieveless particle size
distribution analysis of particulate materials through computer vision,
Computers and Electronics in Agriculture, 2009, 66:147-158), which
reports particle size analyses of several different hammer milled
feedstocks. The measurement may be a volume or a weight average length.

[0045] Washing of the feedstock may be carried out to remove sand, grit
and other foreign particles as they can cause damage to the downstream
equipment.

Feedstock Slurry Preparation

[0046] Slurrying of the feedstock allows it to be pumped readily and may
be carried out in any suitable batch or continuous mixing vessel,
including a standpipe or pulper. Slurrying may be distinct from the water
and chemical addition or may occur simultaneously therewith.

[0047] Slurrying can occur at any suitable consistency selected by those
of ordinary skill in the art. However, in practice, the consistency of
the feedstock slurry utilized will depend on the specific mixing means
employed and the specific pumps used. In one embodiment of the invention,
the consistency of the feedstock slurry is between about 2 wt % and about
40 wt % or more typically between about 4 wt % and about 20 wt %.

[0048] The consistency of the aqueous slurry of the lignocellulosic
feedstock is expressed as the undissolved solids concentration (UDS).
Reference may be made to the "Handbook of Industrial Mixing" (Ed. Paul,
Atiemo-Obeng, Kresta, 2004, Wiley-Interscience, Hoboken, N.J.,
incorporated herein by reference), which provides an introduction to the
equipment and critical parameters of mixing performance and design. (See,
for example, Chapters 10, 17 and 18 that particularly focus on
solid-liquid mixing).

Dewatering Prior to Pretreatment

[0049] After slurrying, leaching and/or soaking, the lignocellulosic
feedstock may subsequently be dewatered by any suitable technique known
to those of ordinary skill in the art. For instance, dewatering may be
effected by utilizing devices that remove water under pressure from the
aqueous feedstock slurry. Dewatering devices suitable for use in the
invention include pressurized screw presses, such as those described in
WO 2010/022511 (incorporated herein by reference) and pressurized
filters. The dewatering process optionally includes a pre-draining zone
in order to drain out water from the feedstock slurry at atmospheric
pressure or higher. This dewatered feedstock slurry is then sent to one
or more devices for dewatering the slurry under pressure. Water expressed
from the lignocellulosic feedstock by the dewatering step may be reused
in the process.

Pretreatment of the Lignocellulosic Feedstock

[0050] As used herein, a "pretreated lignocellulosic feedstock" or
"pretreated feedstock` is a lignocellulosic feedstock that has been
subjected to physical and/or chemical processes to make the fiber more
accessible and/or receptive to the actions of cellulolytic enzymes or to
subsequent chemical treatment to hydrolyze cellulose.

[0051] The pretreatment generally disrupts the fiber structure of the
lignocellulosic feedstock and increases the surface area of the feedstock
to make it accessible to cellulase enzymes. Preferably, the pretreatment
is performed so that a high degree of hydrolysis of the xylan and only a
small amount of conversion of cellulose to glucose occurs. The cellulose
is hydrolyzed to glucose in a subsequent step that uses cellulase
enzymes.

[0052] The extent of xylan hydrolysis may be between about 80 and 100 wt
%, or any range therebetween. A suitable pH and temperature can be
selected within this pH range to hydrolyze at least about 80% of the
xylan, while maintaining the degree of cellulose hydrolysis at about 3 to
about 15 wt %.

[0053] The acid pretreatment is preferably carried out at a temperature of
about 160° C. to about 280° C. It should be understood
that, in practice, there will be a time delay in the pretreatment process
before the feedstock reaches this temperature range. Thus, the above
temperatures correspond to those values reached after sufficient
application of heat to reach a temperature within this range. The time
that the feedstock is held at this temperature may be about 6 seconds to
about 3600 seconds, or about 15 seconds to about 750 seconds or about 30
seconds to about 240 seconds.

[0054] The pretreatment is typically carried out under pressure. For
example, the pressure during pretreatment may be between about 50 and
about 700 psig or between about 75 and about 600 psig, or any pressure
range therebetween.

[0055] If acid is employed for pretreatment, it may be sulfuric acid,
sulfurous acid, hydrochloric acid or phosphoric acid. Preferably, the
acid is sulfuric acid. The amount of acid added to the lignocellulosic
feedstock may vary, but should be sufficient to achieve a final
concentration of acid in the slurry of about 0.02 wt % to about 2 wt %,
or any amount therebetween. The resulting pH of the feedstock is about pH
0.4 to about pH 3.5, or any pH range therebetween. The feedstock may be
heated with steam during or prior to pretreatment. Without being
limiting, one method to carry this out is to use low pressure steam to
partially heat the feedstock, which is then pumped to a heating train of
several stages. Other means may be employed to heat the feedstock, such
as commercially available mixing devices designed for introducing steam
and optionally acid through spray nozzles.

[0056] Without being limiting, pretreating of the feedstock slurry
preferably involves continuous pretreatment, meaning that the
lignocellulosic feedstock is pumped through a reactor continuously.
Continuous acid pretreatment is familiar to those skilled in the art;
see, for example, WO 2006/128304 (Foody and Tolan).

[0057] The use of organic liquids in pretreatment may be used in the
invention as described by Converse et al., (U.S. Pat. No. 4,556,430) and
has the advantage that the low boiling point liquids can easily be
recovered and reused. Other pretreatments, such as the Organosolv®
process, also use organic liquids.

[0058] The acid pretreatment produces a composition comprising an acid
pretreated feedstock. Sugars produced by the hydrolysis of hemicellulose
during acid pretreatment are generally present in the composition and
include xylose, glucose, arabinose, mannose, galactose or a combination
thereof. Organic acids may be present in the composition as well and may
include acetic acid, galacturonic acid, formic acid, lactic acid,
glucuronic acid or a combination thereof. Many lignocellulosic feedstocks
contain hemicellulose with acetyl groups attached to xylan. Pretreatment
processes liberate acetic acid from the acetyl groups.

[0059] According to one exemplary embodiment of the invention, the soluble
components of the pretreated feedstock composition are separated from the
solids. This separation may be carried out by washing the pretreated
feedstock composition with an aqueous solution to produce a wash stream,
and a solids stream comprising the unhydrolyzed, pretreated feedstock
and/or by using solids-liquid separation techniques. The aqueous stream,
which includes the sugars released during pretreatment, the pretreatment
chemical and other soluble components, may then be fermented using a
microorganism capable of fermenting the sugars derived from the
hemicellulose component of the feedstock.

[0060] Pretreatment may also be carried out under alkaline conditions.
Examples of suitable alkaline pretreatment processes include ammonia
fiber expansion (AFEX) or dilute ammonia pretreatment.

[0061] According to the AFEX process, the cellulosic biomass is contacted
with ammonia or ammonium hydroxide, which is typically concentrated, in a
pressure vessel. The contact is maintained for a sufficient time to
enable the ammonia or ammonium hydroxide to swell (i.e., decrystallize)
the cellulose fibers. The pressure is then rapidly reduced which allows
the ammonia to flash or boil and explode the cellulose fiber structure.
The flashed ammonia may then be recovered according to known processes.
The AFEX process may be run at about 20° C. to about 150°
C. or at about 20° C. to about 100° C. and all temperatures
therebetween. The duration of this pretreatment may be about 1 minute to
about 20 minutes, or any time therebetween.

[0062] Dilute ammonia pretreatment utilizes more dilute solutions of
ammonia or ammonium hydroxide than AFEX. Such a pretreatment process may
or may not produce any monosaccharides. Dilute ammonia pretreatment may
be conducted at a temperature of about 100 to about 150° C. or any
temperature therebetween. The duration for such a pretreatment may be
about 1 minute to about 20 minutes, or any time therebetween.

[0063] The concentration of pretreated lignocellulosic feedstock in the
slurry depends on the particle size, water retention, pump capacity and
other properties of the feedstock. Typically, the concentration is
between about 3% and about 30% (w/w), or any amount therebetween of fiber
solids (also known as suspended or undissolved solids), or between about
10% and about 30% (w/w) fiber solids, or any amount therebetween. The
fiber solids concentration may depend on whether dewatering of the
feedstock slurry is carried out prior to pretreatment, for example as set
forth in WO 2010/022511 (incorporated herein by reference).

[0064] Subsequent to pretreatment, the pretreated feedstock slurry is
typically cooled to decrease its temperature to a range at which the
cellulase enzymes are most active. Cooling of the feedstock can occur in
a number of stages utilizing flashing, heat exchange or other suitable
means.

[0065] Flashing removes steam and volatiles from the system. For example,
from 1 to about 8 successive flashing stages, or any amount therebetween,
can be performed. The multiple flashing stages generate flash steam at
different pressures. The steam from flashing can be used as a source of
steam in the plant. For example, flash steam may supply steam to a
downstream evaporator unit or be used for cleaning or disinfecting.

[0066] Steam from the flash tanks may also be used to indirectly preheat
process streams, resulting in the production of flash condensate. For
example, flash steam may be used on one side of a heat exchanger to
preheat boiler feed water on the other side of the heat exchanger,
thereby producing preheated boiler feed water and flash condensate.
Similarly, the flash condensate itself can also be used to indirectly
preheat process stream. Flash steam may also be cooled with cooling
water, chilled water, or other sources of water to produce flash
condensate if it is not convenient to preheat other streams. Once
created, the flash condensate may then be sent to the treatment process
of the invention, as described below.

Enzymatic Hydrolysis and Enzyme Fermentation

[0067] The enzymatic hydrolysis of the cellulose to soluble sugars can be
carried out with any type of cellulase enzymes suitable for such purpose
and effective at the pH and other conditions utilized, regardless of
their source. Among the most widely studied, characterized and
commercially produced cellulases are those obtained from fungi of the
genera Aspergillus, Humicola, Chrysosporium, Melanocarpus,
Myceliophthora, Sporotrichum and Trichoderma, and from the bacteria of
the genera Bacillus and Thermobifida. Cellulase produced by the
filamentous fungi Trichoderma longibrachiatum comprises at least two
cellobiohydrolase enzymes termed CBHI and CBHII and at least four EG
enzymes. As well, EGI, EGII, EGIII, EG V and EGVI cellulases have been
isolated from Humicola insolens (see Lynd et al., 2002, Microbiology and
Molecular Biology Reviews, 66(3):506-577 for a review of cellulase enzyme
systems and Coutinho and Henrissat, 1999, "Carbohydrate-active enzymes:
an integrated database approach." In Recent Advances in Carbohydrate
Bioengineering, Gilbert, Davies, Henrissat and Svensson eds., The Royal
Society of Chemistry, Cambridge, pp. 3-12, each of which are incorporated
herein by reference).

[0068] The conversion of cellobiose to glucose is carried out by the
enzyme β-glucosidase. By the term "β-glucosidase", it is meant
any enzyme that hydrolyzes the glucose dimer, cellobiose, to glucose. The
activity of the β-glucosidase enzyme is defined by its activity by
the Enzyme Commission as EC#3.2.1.21. The β-glucosidase enzyme may
come from various sources; however, in all cases, the β-glucosidase
enzyme can hydrolyze cellobiose to glucose. The β-glucosidase enzyme
may be a Family 1 or Family 3 glycoside hydrolase, although other family
members may be used in the practice of this invention. The preferred
β-glucosidase enzyme for use in this invention is the Bgl1 protein
from Trichoderma reesei. It is also contemplated that the
β-glucosidase enzyme may be modified to include a cellulose binding
domain, thereby allowing this enzyme to bind to cellulose.

[0069] In addition to CBH, EG and beta-glucosidase, there are several
accessory enzymes that aid in the enzymatic digestion of cellulose (see
co-owned WO 2009/026722 (Scott), which is incorporated herein by
reference, and Harris et al., 2010, Biochemistry, 49:3305-3316). These
include EGIV, also known as Cel61, swollenin, expansin, lucinen and
cellulose-induced protein (Cip). Glucose can be enzymatically converted
to the dimers gentiobiose, sophorose, laminaribiose and others by
beta-glucosidase via transglycosylation reactions.

[0070] Cellulase enzyme mixtures used to hydrolyze cellulose are produced
in an enzymatic fermentation. The fermentation to produce the cellulase
enzymes can be conducted with any of the previously mentioned organisms.
The fermentation may be conducted in an enzyme production facility
located in close proximity to the ethanol production facility, such that
the enzyme product can be transported via pipeline to the ethanol
production facility. Alternatively, the enzyme production facility may be
in a different geographical location from the ethanol production
facility, with the enzyme product being shipped to the ethanol production
facility.

[0071] The enzymatic fermentation requires both an organic carbon source
as well as nutrients necessary to support growth and enzyme production.
It may be a simple or complex carbon source, purified or unpurified,
containing carbon source(s) including, but not limited to, glucose,
xylose, mannose, galactose, fructose, sucrose, dextrose, glycerol, or
methanol. The carbon source will also generally contain a secondary
carbon source that induces enzyme production from the fermenting
organism. Some examples of inducing compounds include but are not limited
to cellulose, cellobiose, gentiobiose and sophorose.

[0072] The nutrients required for growth and enzyme production are those
typically associated with the growth of any microbial fermentation. For
example, nutrients added to the fermentation may include yeast extract,
corn steep liquor, specific amino acids, phosphate, nitrogen sources,
salts, trace elements and vitamins.

[0073] The fermentation process is typically a sterile process, meaning
all components of the fermentation equipment and media ingredients that
come in contact with the fermentation broth are heat treated with steam,
either directly or indirectly, to eliminate the presence of any
microorganisms other than the production microorganism. The fermentation
may be operated in a fed-batch or continuous mode.

[0074] The fermentation is generally conducted at a temperature of about
20° C. to about 45° C., or between about 25° C. and
about 35° C., or any temperature therebetween and at a pH of
between about 3.0 and about 6.0 or between about 3.5 and about 5.5, or
any pH therebetween. Furthermore, the fermentation is generally operated
in an aerobic regime, with sterile-filtered air supplied to the vessel to
maintain a dissolved oxygen level in the vessel that is measured above
0%. For example, the dissolved oxygen level, as measured in the
fermentation broth at any point during the fermentation process may be
between about 1% and about 90% of saturation.

[0075] Once the enzyme fermentation is complete, the broth containing both
enzymes and biomass of the fermenting organism is transferred to a
storage vessel. From there, depending on the location of the enzyme
production facility, and the location of the ethanol facility, the broth
can be transferred directly to the ethanol facility for use in the
hydrolysis system through a pipeline. Alternatively, the fermentation
broth can be further processed before being sent to the ethanol
production facility for use in the hydrolysis system.

[0076] Further processing steps may be conducted to change any number of
characteristics in the enzyme product stream as per requirements of the
ethanol production facility or other uses thereof. This includes, but is
not limited to, separating the enzyme from the fermenting organism in the
enzyme product stream, reducing the concentration of other microorganisms
in the product stream, increasing the concentration of enzyme in the
product stream through concentration and reducing the concentration of
other components in the stream, such as unconsumed components. Measures
may be taken to improve storage and shelf life, including stabilizing the
product stream by the addition of sucrose, glycerol and sorbitol,
preserving the product stream to improve shelf life or packaging the
enzyme into discrete containers for transport to the ethanol facility
and/or for prolonged storage. Equipment used to further process the
product stream may include, but is not limited to, filter presses, plate
and frame presses, centrifuges, decanters, microfilters, ultrafilters,
and reverse osmosis units. Components that may be added to the enzyme
product stream may include, but are not limited, to sodium benzoate,
potassium sorbate, phosphoric acid, sodium hydroxide, caramel colour, and
sucrose.

[0077] The enzyme produced in the fermentor is then used to hydrolyze
cellulose in the pretreated feedstock. The amount of enzyme supplied to
the ethanol production facility depends on the production rate of the
ethanol production facility, and the activity of the enzyme being
supplied. An appropriate cellulase dosage can be about 1.0 to about 40.0
Filter Paper Units (FPU or IU) per gram of cellulose, or any amount
therebetween. The FPU is a standard measurement familiar to those skilled
in the art and is defined and measured according to Ghose (Pure and Appl.
Chem., 1987, 59:257-268; which is incorporated herein by reference). A
preferred cellulase dosage is about 10 to about 20 FPU per gram
cellulose.

[0078] The enzymatic hydrolysis is generally conducted at a pH between
about 4.0 and about 6.0 as this is within the optimal pH range of most
cellulases. If acid pretreatment is utilized, the pH of the feedstock
will be increased with alkali to about pH 4.0 to about 6.0 prior to
enzymatic hydrolysis, or more typically between about 4.5 and about 5.5.
However, cellulases with pH optima at more acidic and more alkaline pH
values are known.

[0079] The alkali can be added to the pretreated feedstock after it is
cooled, before cooling, or at points both before and after cooling. The
alkali may be added in-line to the pretreated feedstock, such as an
in-line mixer, to a pump downstream of pretreatment or directly to a
hydrolysis vessel. The point of alkali addition can coincide with the
cellulase enzyme addition, or it can be added upstream or downstream of
the location of the enzyme addition.

[0080] The temperature of the slurry is adjusted so that it is within the
optimum range for the activity of the cellulase enzymes. Generally, a
temperature of about 45° C. to about 70° C., or about
45° C. to about 65° C., or any temperature therebetween, is
suitable for most cellulase enzymes. However, the temperature of the
slurry may be higher for thermophilic cellulase enzymes.

[0081] In order to maintain the desired hydrolysis temperature, the
hydrolysis reactors may be jacketed with steam, hot water, or other heat
sources. Moreover the reactors may be insulated to retain heat.

[0082] It is preferred that enzymatic hydrolysis and fermentation are
conducted in separate vessels so that each biological reaction can occur
at its respective optimal temperature. However, the hydrolysis of the
invention may be conducted simultaneously with fermentation in a
simultaneous saccharification and fermentation (SSF). SSF is typically
carried out at temperatures of 35-38° C., which is a compromise
between the 50° C. optimum for cellulase and the 28° C.
optimum for yeast. Consequently, this intermediate temperature can lead
to substandard performance by both the cellulase enzymes and the yeast.

[0083] Other design parameters of the hydrolysis system may be adjusted as
required. For example, the volume of a hydrolysis reactor in a cellulase
hydrolysis system can range from about 100,000 L to about 30,000,000 L,
for example, between about 200,000 and about 20,000,000 L, or any volume
therebetween, although reactors of large volume may be preferred to
reduce cost. The total residence time of the slurry in a hydrolysis
system may be between about 12 hours to about 200 hours, or any amount
therebetween.

[0084] After the hydrolysis is complete, the product is glucose and any
unreacted cellulose. Insoluble solids present in the resulting stream,
including lignin, may be removed using conventional solid-liquid
separation techniques prior to any further processing. However, it may be
desirable in some circumstances to carry forward both the solids and
liquids in the sugar stream for further processing.

Fermentation

[0085] Fermentation of glucose resulting from the hydrolysis may produce
one or more of the fermentation products selected from an alcohol, a
sugar alcohol, an organic acid and a combination thereof.

[0086] In one embodiment of the invention, the fermentation product is an
alcohol, such as ethanol or butanol. For ethanol production, the
fermentation is typically carried out with a Saccharomyces spp. yeast.
Glucose and any other hexoses present in the sugar stream may be
fermented to ethanol by wild-type Saccharomyces cerevisiae, although
genetically modified yeasts may be employed as well, as discussed below.
The ethanol may then be distilled to obtain a concentrated ethanol
solution. Butanol may be produced from glucose by a microorganism such as
Clostridium acetobutylicum and then concentrated by distillation.

[0087] The fermentation comprises at least fermenting glucose to ethanol.
Xylose and arabinose that are derived from the hemicellulose may
additionally be fermented to ethanol by a yeast strain that naturally
contains, or has been engineered to contain, the ability to ferment these
sugars to ethanol. Examples of microbes that have been genetically
modified to ferment xylose include recombinant Saccharomyces strains into
which has been inserted either (a) the xylose reductase (XR) and xylitol
dehydrogenase (XDH) genes from Pichia stipitis (U.S. Pat. Nos. 5,789,210,
5,866,382, 6,582,944 and 7,527,927 and European Patent No. 450530) or (b)
fungal or bacterial xylose isomerase (XI) gene (U.S. Pat. Nos. 6,475,768
and 7,622,284). Examples of yeasts that have been genetically modified to
ferment L-arabinose include, but are not limited to, recombinant
Saccharomyces strains into which genes from either fungal (U.S. Pat. No.
7,527,951) or bacterial (WO 2008/041840) arabinose metabolic pathways
have been inserted.

[0088] Organic acids that may be produced during the fermentation include
lactic acid, citric acid, ascorbic acid, malic acid, succinic acid,
pyruvic acid, hydroxypropanoic acid, itaconoic acid and acetic acid. In a
non-limiting example, lactic acid is the fermentation product of
interest. The most well-known industrial microorganisms for lactic acid
production from glucose are species of the genera Lactobacillus, Bacillus
and Rhizopus.

[0089] Moreover, xylose and other pentose sugars may be fermented to
xylitol by yeast strains selected from the group consisting of Candida,
Pichia, Pachysolen, Hansenula, Debaryomyces, Kluyveromyces and
Saccharomyces. Bacteria are also known to produce xylitol, including
Corynebacterium sp., Enterobacter liquefaciens and Mycobacterium
smegmatis.

[0090] The fermentation is typically conducted at a pH between about 4.0
and about 6.0, or between about 4.5 and about 6.0. To attain the
foregoing pH range for fermentation, it may be necessary to add alkali to
the stream comprising glucose. A temperature range for the fermentation
of glucose to ethanol can be between about 18° C. and about
35° C.

[0091] In one exemplary embodiment of the invention, the operating
temperature and pH of the fermentation is a balance between the optimum
for the fermenting microorganism and conditions suitable for
contamination management. The fermentation may also be supplemented with
additional nutrients required for the growth of the fermentation
microorganism. For example, yeast extract, specific amino acids,
phosphate, nitrogen sources, salts, trace elements and vitamins may be
added to the hydrolysate slurry to support their growth.

[0092] The fermentation may be conducted in batch, continuous or fed-batch
modes with or without agitation. Preferably, the fermentation reactors
are agitated lightly with mechanical agitation. A typical,
commercial-scale fermentation may be conducted using multiple reactors.
The fermentation microorganisms may be recycled back to the fermentor or
may be sent to distillation without recycle. If recycle of the yeast is
desirable, then a filtration step, as described below, is conducted prior
to the fermentation to remove suspended solids from the hydrolysate,
thereby enabling recycle of the yeast within fermentation.

Distillation

[0093] If ethanol or butanol is the fermentation product, the recovery is
carried out by distillation, typically with further concentration by
molecular sieves or membrane extraction. If there is no cell recycle in
fermentation, the fermentation broth that is sent to distillation is a
dilute alcohol solution containing solids, including unconverted
cellulose, and any components added during the fermentation to support
growth of the microorganisms. If cell recycle is employed in
fermentation, then the fermentation broth will not contain a significant
level of suspended solids.

[0094] Microorganisms are potentially present during the distillation
depending upon whether or not they are recycled during the fermentation.
The broth is preferably degassed to remove carbon dioxide and then pumped
through one or more distillation columns to separate the alcohol from the
other components in the broth. The mode of operation of the distillation
system depends on whether the alcohol has a lower or a higher boiling
point than water. Most often, the alcohol has a lower boiling point than
water, as is the case when ethanol is distilled.

[0095] The column(s) in the distillation unit is preferably operated in a
continuous mode, although it should be understood that batch processes
are also encompassed by the present invention. Heat for the distillation
process may be introduced at one or more points either by direct steam
injection or indirectly via heat exchangers. The distillation unit may
contain one or more separate beer and rectifying columns, in which case
dilute beer is sent to the beer column where it is partially
concentrated. From the beer column, the vapour goes to a rectification
column for further purification. Alternatively, a distillation column is
employed that comprises an integral enriching or rectification section.

[0096] An aqueous stream(s) remaining after ethanol distillation and
containing solids, referred to herein as "still bottoms", is withdrawn
from the bottom of one or more of the column(s) of the distillation unit.
This stream will contain inorganic salts, unfermented sugars and organic
salts. Lignin may be present as well if it is not removed prior to
distillation.

[0097] When the alcohol has a higher boiling point than water, such as
butanol, the distillation is run to remove the water and other volatile
compounds from the alcohol. The water vapor exits the top of the
distillation column and is known as the "overhead stream".

Alcohol Concentration

[0098] After ethanol distillation, the remaining water is removed from the
alcohol-enriched vapour by an azeotropic breaking process to produce a
concentrated alcohol solution. The term azeotropic breaking process or
azeotrope breaking system is meant to encompass any process for breaking
the azeotrope of the alcohol-enriched vapour. This includes, but is not
limited to, feeding the alcohol-enriched vapour to molecular sieves.
Other azeotropic breaking processes that are encompassed by this
definition include pervaporation and the addition of benzene or
cyclohexane to a distillation column. After breaking the azeotrope to
obtain the concentrated alcohol solution, the vapour is typically
condensed to product alcohol and then denatured. If benzene or
cyclohexane is used to break the azeotrope, they may be added to a
distillation column to which the alcohol-enriched vapour is fed and acid
may be added into such distillation column to reduce the concentration of
ammonia in the alcohol-enriched vapour within said distillation column.

[0099] Preferably, the azeotropic breaking process utilizes molecular
sieves. In this case, reducing the concentration of ammonia in the
alcohol-enriched vapour stream reduces or prevents fouling or capacity
loss of the desiccant. Any of a variety of known molecular sieves (also
referred to as molecular sieve dehydrators) may be used in the practice
of the invention. Molecular sieves on the market contain a zeolite
material that have a crystalline lattice structure that contains openings
(pores) of a precise size, usually measured in angstroms (Å). Pore
sizes that are suitable will depend on the alcohol to be concentrated.
Preferred zeolites for use with ethanol-enriched vapour are those of type
3 Å since the pores are 3 Å in diameter while water molecules are
2.8 Å and ethanol molecules are 4.4 Å. Furthermore, other
adsorbent materials besides zeolites are available that have an affinity
for water such as activated alumina. Although these adsorbents may be
utilized in the practice of the invention, zeolite materials are
preferred since they are typically more selective.

[0100] As would be appreciated by those of skill in the art, molecular
sieves commonly use "pressure swing adsorption" to remove water from a
vapourized feed stream. This refers to the fact that the molecular sieve
uses a relatively high pressure when water is being removed from the feed
stream and a relatively low pressure when the molecular sieve desiccant
is being regenerated, i.e., having water removed from the desiccant.
Typical commercial designs have two or more beds of desiccant and cycle
the vapour flow through the beds to provide continuous operation. (See
Development and operation of the molecular sieve: an industry standard,
R. L. Bibb Swain, The Alcohol Textbook, 4th Edition, Nottingham
University Press, 2003, pages 337-342). For example, during operation, a
molecular sieve may be drying the feed vapour, while another is being
regenerated (i.e., water is removed so that the desiccant is ready for
the next feed cycle).

Still Bottoms Processing

[0101] If the still bottoms from distillation comprise lignin, they may be
subjected to lignin separation to remove lignin and other converted
undissolved solids therefrom. Lignin separation may be conducted by
utilizing a filter press, or other known solids-liquid separation
equipment. The separated lignin may be subsequently sent to a boiler.

[0102] Still bottoms from distillation may be sent to an evaporator unit.
If the still bottoms are subjected to the lignin separation step, the
separated liquid component may be fed to the evaporation unit. Here, the
still bottoms are concentrated and the evaporated liquid is condensed by
cooling. The evaporator condensate, in turn, may be sent to the treatment
process, and then recycled, as discussed in more detail below. Typically,
the evaporator condensate is cooled prior to the treatment process, with
the heat optionally used to preheat a process stream elsewhere in the
process.

[0103] The evaporator condensate may be combined with other condensates
and process streams. The condensates are typically collected in a tank.

[0104] The still bottoms contain components that can be recovered as
co-products, as discussed below. Evaporation of the still bottoms can
allow for more efficient extraction of these co-products.

[0105] In one embodiment of the invention, the evaporator unit is a
multiple-effect evaporator. The evaporation may be carried out in a
single-stage evaporator or may be part of a multiple-effect system, i.e.,
a system in which more than one evaporator is employed. Multiple-effect
evaporator systems are preferred as they can reduce heating requirements
and the resultant energy usage. A total of 3 to 7 effects are preferred
to achieve the optimum steam economy. A multiple-effect evaporator system
utilized in accordance with the invention can be forward fed, meaning
that the feeding takes place so that the solution to be concentrated
enters the system through the first effect, which is at the highest
temperature. Partial concentration occurs in the first effect, with
vapour sent to the second effect to provide heat for same. The partially
concentrated solution is then sent to the second effect where it is again
partially concentrated, with vapour sent to the third effect, and so on.
Alternatively, backward feeding may be utilized, in which the partially
concentrated solution is fed from effect to effect with increasing
temperature.

[0106] Those of skill in the art can readily choose a suitable operating
temperature for the evaporator unit. In embodiments of the invention, the
operating temperature of the evaporator unit can be between about
40° C. and about 145° C. It will be understood that the
temperature is measured under the operating pressure, which is typically
under vacuum or at atmospheric pressure, but can be at higher pressure.
Co-products can be recovered from the condensate. For example, acetic
acid can be recovered from the condensate by liquid-liquid extraction
using conventional processes. This technique may involve using a solvent
to extract acetic acid from the feed stream, followed by distillation
stages for dehydration, solvent recovery and acid purification. One or
more of the bottom products from these distillation stages can be sent to
the anaerobic digester and then water obtained from the anaerobic
treatment can be recycled into the process.

Inhibitors

[0107] As discussed, streams derived from lignocellulosic feedstocks
contain a number of compounds that are inhibitory to the microorganism in
the fermentation or cellulase enzymes. Furan derivatives such as
2-furaldehyde (furfural) and 5-hydroxymethyl-2-furaldehyde (HMF) are
inhibitory compounds that originate from the breakdown of the
carbohydrate fraction, namely xylose and glucose, respectively.
Additional organic acids found in the process streams that may be
inhibitory to yeast or other microorganisms include galacturonic acid,
lactic acid, glucuronic acid, 4-O-methyl-D-glucuronic acid or a
combination thereof. Inhibiting phenolic compounds are also produced by
the degradation of lignin, which include vanillin, syringaldeyhde, and
hydroxybenzylaldehyde. In particular, vanillin and syringaldehyde are
produced via the degradation syringyl propane units and guaiacylpropane
units of lignin (Jonsson et al., 1998, Appl. Microbiol. Biotechnol.
49:691).

[0108] Acetic acid is a component of process streams produced from
lignocellulosic material that is highly inhibitory to yeast and cellulase
enzymes. The acetate arises from acetyl groups attached to xylan and
lignin that are liberated as acetic acid and/or acetate by exposure to
acid or other chemicals that hydrolyze the feedstock. (Abbott et al.,
2007, FEMS Yeast Res. 7:819-833; Hu et al., 2009, Bioresource Technology
100:4843-4847; and Taherzadeh et al., 1997, Chem Eng Sci, 52:2653-5659).

[0109] Kellsall and Lyons ("The Alcohol Textbook", Ed. K. Jaeques, T. P.
Lyons and D. R. Kelsall, 1999, Nottingham University Press, Nottingham,
United Kingdom, incorporated herein by reference) disclose that acetic
acid levels at or above 0.05 wt % are known to be inhibitory to yeast.
However, the inhibition in cellulosic conversion processes to produce
ethanol or other fermentation products is a more significant problem than
corn ethanol fermentation as, depending on the pretreatment conditions
and the composition of the feedstock, acetic acid levels in the feed
stream to fermentation can range from about 0.1 to about 1.2 wt %, which
is between about 6 and about 70 times more concentrated than the corn
ethanol process and above known inhibition levels. Cellulosic ethanol
conversion processes are also susceptible to contamination, which can add
more acetic acid.

[0110] Thus, according to embodiments of the invention, the stream
subjected to the step of fermenting contains about 0.1 to about 1.2 wt %
acetic acid (including acetate species), or any range therebetween. For
example, the stream subjected to fermentation may contain up to about
0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1 or 1.2 wt % acetic
acid.

[0111] The inhibitory compounds set forth above are representative of the
compounds present in a process stream produced from a lignocellulosic
feedstock. It will be appreciated that the inhibitory compounds present
depend on both the raw material and the pretreatment that is employed.

Process Streams Fed to the Treatment Process

[0112] The process stream(s) selected for further treatment in the
treatment process, described in more detail below, and subsequent
recycle, may contain reduced levels of inhibitors and/or other
undesirable components relative to other streams generated in the
process. Examples of such streams are provided in FIG. 1.

[0113] As shown in FIG. 1, the one or more process streams 2 for treatment
may be obtained from a cellulosic conversion process 1, associated
utilities 3 and/or from seal water 4. Process streams 2 obtained from the
cellulosic conversion process 1 include spent cleaning solution,
condensate streams and rectifier effluent. Those streams obtained from
the associated utilities, such as a boiler or cooling tower, may include
blowdowns and regenerated streams. Spent seal water can also be obtained
from seal water 4. Each of these process streams are described in turn
below.

A. Spent Cleaning Solution

[0114] Process equipment utilized during the cellulosic conversion process
may be prone to scale or solids build-ups during operation of the
cellulosic conversion process. A cleaning regime utilizing an appropriate
cleaning solution may be employed to remove such build-ups and the
resultant spent cleaning solution can be treated and re-circulated in the
process. Pretreatment, hydrolysis, enzyme or ethanol fermentation and
distillation equipment and solid-liquid separators are examples of
process equipment that may require treatment with a cleaning solution.
Furthermore, a cleaning solution may be utilized to sanitize process
equipment, for example during fermentation, as discussed below.

[0115] As used herein, the term "spent cleaning solution" refers to any
solution previously used to clean one or more pieces of process equipment
in the cellulosic conversion process. The term includes any suitable
solution used to clean process equipment for the purpose of scale
removal, debris removal, disinfection, decontamination, or any other
purpose as required. This includes alkali or acidic solutions. Spent
cleaning solution may be generated in several of the processing steps in
the production of ethanol or other fermentation products from cellulose,
including but not limited to pretreatment, hydrolysis, enzyme or ethanol
fermentation, distillation, filtration and evaporation.

[0116] In one embodiment of the invention, the solids or scale can be
removed by cleaning with one or more cleaning solutions comprising either
alkali or acid at elevated temperatures. In one embodiment the
temperature is between about 50° C. and about 250° C., or
between about 60° C. and about 220° C., or between about
60° C. and about 150° C., or between about 60° C.
and about 95° C., or any temperature range therebetween. The
temperature and chemical make-up of the cleaning solution will vary
depending on the scale that is being treated.

[0117] Non-limiting examples of alkali that may be used in the practice of
the invention include those selected from the group consisting of sodium
hydroxide, potassium hydroxide, ammonia, ammonium hydroxide, potassium
carbonate, potassium bicarbonate, sodium carbonate and sodium
bicarbonate. In one embodiment of the invention, the alkali is sodium
hydroxide or potassium hydroxide. In yet another embodiment of the
invention, the alkali is sodium hydroxide.

[0118] Non-limiting examples of acid that may be used in the practice of
the invention include those selected from the group consisting of
phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid and
sulfurous acid. In one embodiment of the invention, the acid is
phosphoric acid or sulfuric acid. In yet another embodiment of the
invention the acid is phosphoric acid.

[0119] During fermentation, washing solutions can be employed to disinfect
surfaces that are prone to contamination by microorganisms. Such
solutions can be alkali or acidic, depending on the purpose of the
treatment.

[0120] An example of scale that can build up in process equipment is
lignin scale. The formation of lignin scale deposit and treatment methods
to remove it, are described in co-owned WO 2011/094859, which is hereby
incorporated by reference.

[0121] During or after the pretreatment process, any equipment that is
exposed to feedstock undergoing a change in physical properties may be
prone to scale deposit comprising lignin. The change in physical
properties may include, but is not limited to, a change in temperature,
pH, concentration, pressure or physical state. Examples of process
equipment that may be prone to scale deposit comprising lignin include,
but are not limited to, pumps; pipes; heat exchangers; in-line or other
mixing equipment, including steam mixers; valves; agitators; scrapers;
vessels and vessel internals, including but not limited to baffles,
ports, impellors, spargers, and sampling devices; filtration units,
including but not limited to pressure filters, microfilters,
ultrafilters, nanofilters and reverse osmosis units; and conveyors.

[0122] Lignin scale can generally be removed with an alkali solution at
elevated temperatures. The concentration of the alkali may be between
about 0.5 wt % and about 10 wt %, or between about 0.5 and about 6 wt %,
or between about 1 and about 5 wt %. The temperature required to remove
the scale may be between about 50 and about 150° C., or between
about 65° C. and about 120° C., or between about 75°
C. and about 120° C. Higher temperatures can be utilized as well,
including between about 120° C. and about 250° C.

[0123] In addition to lignin scale, fermentation equipment is prone to
other types of scale formation. This scale can include but is not limited
to the build-up of microbial cells, including yeast, fungus or bacterial
biomass, biofilms, protein scale, inorganic scale and organic scale
formation. In addition to treatment with alkali at elevated temperatures
for lignin removal, these scales can be removed with acid at elevated
temperatures. The concentration of the acid may be between about 0.5 wt %
and about 5 wt %, or between about 1 and about 5 wt %. The temperature
required to remove the scale may be between about 50 and about
150° C., or between about 65° C. and about 120° C.,
or between about 75° C. and about 95° C.

B. Process Condensate Streams

[0124] In one embodiment of the invention, the process stream selected for
treatment prior to re-circulation is a process condensate stream obtained
from a vapour stream that is subsequently condensed. The vapour stream
may be obtained from a thermodynamic separation process, for example from
a stream that has been subjected to a change in pressure, such as a drop
in pressure, or for example by heating a stream.

[0125] Thermodynamic separation processes include those that separate
streams based upon differences in their boiling points and include, but
are not limited to, flash cooling, distillation and evaporation. The
distillation may be an ethanol distillation process, as described
previously, in which case the condensate stream is derived from an
overhead stream.

[0126] In a further embodiment of the invention, the process condensate
stream is an evaporator condensate resulting from a step of evaporating
still bottoms in an evaporator unit and condensing vapour formed in the
unit, as described previously. The still bottoms are concentrated and the
vapour stream is then condensed by cooling. The evaporator condensate is
then sent to the treatment process described herein.

[0127] Table 1 below provides the organic and inorganic content of still
bottoms streams and condensates from a typical cellulosic conversion
process. As can be seen from the table, condensates contain significantly
lower levels of organic and inorganic compounds than still bottoms.

[0128] The concentration of acetic acid (measured as total acetic acid and
acetate species) in the condensate may be between 0 to about 1.5 wt %.
The pH of the still bottoms may be adjusted to influence the
concentration of acetic acid in the evaporator condensate. During
evaporation, some fraction of acetic acid will volatilize, while its
conjugate base, acetate, will remain in solution and will not volatilize.
The pKa of acetic acid is 4.75, which means that at this pH, 50% of the
acetic acid in solution will be in the acid form, and 50% will be in the
acetate form.

[0129] As the pH is increased above 4.75, the fraction of acetic acid that
is present in the acetate form will increase, thereby reducing the
fraction that is acetic acid and consequently the amount of acetic acid
that is present in the evaporator condensate. A typical still bottoms
stream has an acetic acid concentration of about 0.2 to about 1.2 wt %,
while the condensate stream from an evaporation operated at increased pH
will have an acetic acid concentration of only 0 to about 0.8 wt %. Thus,
operating the evaporation at a pH at which all or a large proportion of
the acetic acid is in the acetate form and sending the evaporator
condensate to the treatment process may be desirable to reduce the
organic load to the treatment process, thus reducing its capital and
operating costs. According to such embodiments, the acetic acid (measured
as total acetate and acetic acid species) in the process condensate
stream may be less than about 0.8, 0.7, 0.6, 0.5, 0.4 or 0.3 wt %.

[0130] Conversely, it may also be desirable to lower the pH of the still
bottoms to increase the fraction that is present as acetic acid, thereby
increasing the concentration of acetic acid in the evaporator
condensates. The condensate stream contains fewer chemical species than
the still bottoms thereby making acetic acid recovery more feasible, if
recovery of acetic acid is desirable. Increasing acetic acid in the
condensate stream may also be desirable for reducing the acetic acid
concentration in the still bottoms, if acetic acid interferes with the
downstream processing of this stream. According to such embodiments of
the invention, the acetic acid (measured as total acetate and acetic acid
species) in the process condensate stream may be between about 0.8 wt %
and about 1.5 wt %, between about 1.0 and about 1.3 wt % or any range
therebetween.

[0131] In a further embodiment of the invention, the condensate stream is
a flash cooling condensate resulting from a step of cooling a pretreated
process stream in a flash tank, collecting the flashed stream and
indirectly contacting it with other process streams to produce preheated
process streams and condensed flash condensate. The flash condensate will
also contain levels of acetic acid. Similar to the evaporator
condensates, the concentrations of acetic acid in the flash condensates
can vary depending on the composition in the feedstock, the pH of the
process stream and the temperature of the flashing. For an acidic
pretreatment process of lignocellulosic feedstock, acetic acid (measured
as total acetate and acetic acid species) in the flash condensates can
range from about 0.4 wt % to about 1.0 wt %, or from about 0.5 to about
0.8 wt %.

[0132] In some embodiments of the invention, different process condensate
streams arising from the conversion process are combined and then
subjected to the treatment process of the present invention.

[0133] The condensate stream may be further treated prior to anaerobic or
aerobic treatment by a physical separation, such as reverse osmosis or
filtration, described in more detail hereinafter.

C. Rectifier Effluent

[0134] As discussed above, the distillation unit may contain one or more
separate beer and rectifying columns, in which case dilute beer is sent
to the beer column where it is partially concentrated. From the beer
column, the vapour goes to a rectification column for further
purification.

[0135] Effluent from the rectifier may be sent to the treatment process.
As used herein, the term "rectifier effluent" refers to any stream
obtained from the bottom of a rectification column.

D. Blowdown Streams

[0136] Several utilities which support the production of ethanol or other
fermentation products from a lignocellulosic feedstock generate blowdown
streams. As used herein, a "blowdown stream" is a stream purged to
maintain a suitable composition of a larger stream.

[0137] A blowdown stream typically arises from a cooling tower or a
boiler. For example, a cooling tower generates a blowdown stream in order
to maintain the amount of dissolved solids and other impurities at an
acceptable level, to avoid scale and corrosion within the cooling tower
system. As another example, a boiler generates a blowdown stream to
maintain water parameters within prescribed limits to minimize scale,
corrosion, carry-over, and other specific problems as well as maintain a
low level of suspended solids within the system.

E. Regenerated Streams

[0138] As used herein, the "regenerated stream" refers to any stream
resulting from regenerating a membrane or a resin used in a separation
process. The separation process may include but is not limited to an ion
exchange process or a reverse osmosis process.

[0139] In one embodiment of the invention the regenerated stream sent to
the treatment process is a waste stream from a water treatment process.
This may include, but is not limited to, the waste stream from a reverse
osmosis unit used to purify fresh water, a waste stream from a water
softener, used to soften water, or any other waste stream from a process
to purify water.

F. Spent Seal Water

[0140] Many pieces of equipment used in the cellulosic conversion process
contain mechanical seals. These devices form a seal between rotating
surfaces, and may be included in any equipment with rotating parts,
including, but not limited to, pumps, agitators, screw presses,
compressors and mixers. Seal water is used to describe water that is sent
to a sealing system, such as water used to cool the seal or to displace
product that may have poor properties for use in a mechanical seal.

[0141] As used herein, "seal water" refers to any water that enters and
then exits a mechanical seal that is contacted with water. For example,
seal water may arise from a flushing operation utilized so as to ensure
proper functioning of the mechanical seal.

[0142] Seal water should generally be clean water to avoid damage to the
internal components of the mechanical seal, including abrasion, erosion,
corrosion, or any other form of damage to the mechanical seal. Water
introduced as seal water generally leaks externally to the seal, although
internal leaking seals are also possible. If the mechanical seal is
functioning properly, then there will be negligible leakage of
contaminating components into the seal water flow, and the externally
leaking seal water flow will consist of clean water. However, if the
mechanical seal is not functioning properly, it is possible for internal
process fluid to leak into the seal water, and subsequently leak
externally to the equipment, and would require treatment before discharge
or reuse in the process.

[0143] The number of pieces of equipment requiring seal water can, in many
instances, be significant, resulting in a high demand for clean water to
be used as seal water, and consequently a large volume of used seal water
which requires treatment. Additionally, as equipment sizes increase, the
amount of seal water required per piece of equipment also increases,
which exacerbates the overall demand for seal water, and the subsequent
treatment requirements.

Composition of Process Streams Selected for Treatment

[0144] One or more of the process streams selected for treatment may
contain an organic content of less than about 5 wt % and/or an inorganic
content of less than about 5 wt %.

[0145] For example, the organic content may be less than about 5.0, 4.5,
4.0, 3.5, 3.0, 2.5, 2.0, 1.5, 1.0 or 0.5 wt %. In further embodiments of
the invention, the organic content is about 0.01 to about 5 wt %, or
about 0.01 to about 4.0 wt %, about 0.01 to about 3.0 wt %, or about 0.01
to about 2.5 wt % or about 0.01 to about 2.0 wt %.

[0146] In some embodiments of the invention, the inorganic content is less
than about 5.0, 4.5, 4.0, 3.5, 3.0, 2.5, 2.0, 1.5, 1.0 or 0.5 wt %. In
further embodiments of the invention, the inorganic content is about 0.01
to about 5 wt %, or about 0.01 to about 4.0 wt %, about 0.01 to about 3.0
wt %, or about 0.01 to about 2.5 wt % or about 0.01 to about 2.0 wt %.

[0147] Organic compounds that may be present in the process streams
include organic acids, including, but not limited to, furfural and acetic
acid. Examples of inorganic compounds that may be present in the process
streams include calcium, magnesium and sodium salts.

Treatment Process to Obtain a Treated Water Stream for Re-circulation

[0148] One or more of the foregoing process streams are (A-F) then
subjected to a treatment process. The treatment process produces a
treated water stream that can be re-circulated to the cellulosic
conversion process or associated utilities.

[0149] Many different configurations and treatment options are encompassed
by the present invention. Exemplary configurations for the treatment
process are provided in FIGS. 2, 3A, 3B and 4, described in detail below.
The treatment process of the invention comprises at least a step of
feeding the one or more process streams to an anaerobic digester, an
aerobic digester and/or a reverse osmosis unit. Each unit operation that
may be employed in the treatment process is discussed in turn below.

Anaerobic Digestion

[0150] Anaerobic digestion involves the use of microorganisms to break
down organic material for the purpose of waste management and energy
production, to primarily produce methane and carbon dioxide. A mixed
population of microbes is used to break down the organic material and may
include, although is not limited to, acidogenic bacteria, acid-forming
bacteria (acetogens), and methane-forming archaea (methanogens). Without
being limiting, this consortium of microorganisms typically process
incoming streams through a series of four general steps. These steps
include hydrolysis, a chemical reaction where particulates are
solubilized and large polymers converted into simpler monomers;
acidogenesis, biological reaction where simple monomers are converted
into volatile fatty acids; acetogenesis, a biological reaction where
volatile fatty acids are converted into acetic acid, carbon dioxide, and
hydrogen; and methanogenesis, a biological reaction where acetates are
converted into methane and carbon dioxide, while hydrogen is consumed.

[0151] Anaerobic digesters may be designed and/or operated in a number of
configurations including batch or continuous, mesophilic or thermophilic
temperature ranges, and low, medium or high rate units. The rate refers
to the chemical oxygen demand (COD) feed rate to the unit, high or low
solids content and single or multistage. The choice of configuration will
depend on a number of factors. These may include consideration of the
nature of the feedstock to be treated, the level of treatment desired
and/or required, capital, operating and maintenance cost considerations,
including consideration of the equipment footprint. Other factors that
may be considered in the configuration choice include operating
parameters, including, but not limited to, residence time, temperature,
pH and the nutrients supplied to the system.

[0152] One of the main products of anaerobic digestion is biogas which is
produced during the final stage of the digestion process, methanogenesis.
Biogas contains methane, which can be combusted to produce both heat and
electricity. Excess electricity can be sold to suppliers or to the local
grid.

Aerobic Digestion

[0153] Depending on the quality of the effluent from the anaerobic
digester, it may be suitable for recycle into selected areas of the
cellulosic conversion process, associated utilities and/or seal water
system. However, the effluent stream may also require further treatment
to be suitable for recycle. One possibility for additional treatment is
aerobic digestion.

[0154] Aerobic digestion uses air and a consortium of microorganisms, also
referred to as activated sludge, to reduce biological oxygen demand (BOD)
and/or chemical oxygen demand (COD) in a process stream and produces
treated water and carbon dioxide. Typically, an aerobic digestion system
will include means to separate the treated water from the microbial
consortium.

[0155] Aerobic digestion systems may be designed and/or operated using any
suitable configuration known to those of skill in the art. Conventional
processes typically include at least one aeration tank and at least one
settling tank. There are many possible configurations for activated
sludge processing, including the vessel size, configuration and numbers
of vessels, continuous or batch operating modes, the aeration delivery
method and rate, and the settling and separation method(s) to be used in
the process. In practice, the selected configuration will depend on a
numbers of factors. These may include the nature of the feedstock to be
treated, the level of treatment desired and/or required, capital,
operating and maintenance cost considerations, including consideration of
the equipment footprint. Other factors that may be considered in the
configuration choice include operating parameters, including residence
time, aeration rate, temperature, pH and nutrients supplied to the
system.

[0156] In addition to the conventional configurations, advances in the
treatment of industrial effluents have led to the development of improved
processes, such as the membrane bioreactor (MBR). The MBR, which can be
used anaerobic or aerobic configuration, combines a bioreactor with a
microbial consortium to break down components in the incoming process
streams with a membrane process such as microfiltration or
ultrafiltration. The membranes are submerged in the bioreactor, thereby
replacing the settling tank or similar process in the conventional
activated sludge processes. This configuration provides many benefits
including eliminating the separate separation equipment and reducing
equipment footprint, removing dependence upon settleability
characteristics of the sludge, and allowing operation at higher sludge
concentrations which reduces the volume of the aeration tank thereby
further reducing the footprint required.

Physical Separation

[0157] Depending on the quality of the effluent stream from anaerobic or
aerobic digestion, one or more of these streams may be suitable for
recycle into the cellulosic conversion process, associated utilities or
seal water system. However, the effluent streams from anaerobic or
aerobic digestion may also require further treatment to be suitable for
recycle into the cellulosic conversion process, the associated utilities
and/or the seal water system. This further treatment may comprise any
suitable physical separation process.

[0158] As used herein, a "physical separation" refers to any separation
process in which at least two components are separated from one another
by exploiting differences in their respective physical properties.
Physical properties can include, but are not limited to, density, mass,
solubility, particle size and distribution.

[0159] One example of a suitable physical separation is reverse osmosis.
Reverse osmosis is a filtration method that removes many types of large
molecules and ions from solutions by applying pressure to the solution
when it is on one side of a selective membrane. The result is that the
solute is retained on the pressurized side of the membrane and the pure
solvent is allowed to pass to the other side. To be selective, this
membrane does not allow large molecules or ions through the pores
(holes), but allows smaller components of the solution (such as the
solvent) to pass freely. Reverse osmosis involves a diffusive mechanism
so that separation efficiency is dependent on solute concentration,
pressure and water flux rate.

[0160] In addition to or instead of reverse osmosis, other types of
physical separation can be used. Physical separation may be employed to
remove larger debris or solids from a stream, or to remove very small
particles or molecules from the stream. A variety of physical separation
filtration equipment types are available, and the choice of technology
will depend on a number of factors including, but not limited to, the
identity and size of the material to be removed, the level of removal
required, and capital, operating and maintenance cost considerations.
Some of the types of physical separation technology that may be employed
include, but are not limited to, filter presses, plate and frame presses,
decanters, centrifuges, settling tanks, clarifiers, microfilters,
ultrafilters, and nanofilters. One or more of these may be used to treat
effluent from an anaerobic or an aerobic digestion process or a reverse
osmosis system.

Chemical Treatments

[0161] In addition to, or instead of aerobic digestion or physical
separation, chemical treatment methods can also be utilized to treat
streams. As used herein, "chemical treatment" refers to any treatment
that may be employed to alter or change the chemical composition of
components of the stream. The chemical treatment can be a chemical
separation technique, an example of which is a chemical separation by ion
exchange. Ion exchange is a separation technique in which an ion from
solution is exchanged for a similarly charged ion attached to an immobile
solid particle. The ion exchange resins may be cation exchangers that
have positively charged mobile ions available for exchange, or anion
exchangers, whose exchangeable ions are negatively charged. The solid ion
exchange particles may be either naturally occurring inorganic zeolites
or synthetically produced organic resins.

[0162] Another example of a chemical separation technique is chemical
precipitation. With chemical precipitation specific chemicals are added
to react with species in solution to form new chemical compounds which
are not soluble under the conditions of the precipitation. The new
chemicals precipitate out of solution as solids, and can then be removed
by standard physical separation techniques.

[0163] Other examples of chemical treatment methods may include but are
not limited to ultraviolet light treatment or treatment with ozone.

Segregation of Streams for Treatment

[0164] In addition to selecting streams with lower levels of inhibitors
for treatment and recycle, the invention involves the segregation of the
selected streams for treatment according to the type and level of
treatment required. By segregating the streams and subjecting them to the
minimum level of treatment required to reduce inhibitor levels, such that
the performance of the biocatalysts in the process are maintained, the
overall capital and operating treatment costs can be reduced. By the term
"segregation", it is meant to set apart or isolate certain process
streams from others based on treatment requirements. The definition also
includes combining certain streams based on their treatment requirements
and segregating those combined streams.

[0165] Rather than segregating process streams, all of the streams can be
combined and sent to anaerobic and then aerobic treatment (e.g., FIG. 2).
Although this configuration will ensure sufficient treatment of the
overall stream, the extent of treatment required and the size of the
treatment equipment needed for the treatment can be cost prohibitive.
Segregation of streams in accordance with the invention overcomes these
limitations.

[0166] In some embodiments of the invention, it is advantageous to send
those streams that require only anaerobic treatment to an anaerobic
treatment system, and those streams that require only aerobic treatment
to an aerobic treatment system. This minimizes the size of both treatment
systems only to what is necessary to provide streams with suitable levels
of inhibition for recycle.

[0167] In yet further embodiments of the invention, aerobic treatment may
not be necessary. For example, process condensate streams will typically
contain organic compounds, which can potentially be treated by anaerobic
digestion or by aerobic digestion. Aerobic digestion provides a higher
level of treatment but at a higher cost. For some condensate streams,
anaerobic treatment will be sufficient to reduce the inhibition level,
and in these cases it would be most advantageous to only treat with an
anaerobic digester prior to recycle, and avoid the cost of aerobic
treatment altogether. However, for other condensate streams, aerobic
treatment may be required to sufficiently reduce the inhibitory compounds
in the stream such that they are suitable for recycle.

[0168] It is also possible that effluent from an anaerobic digester, or a
portion thereof, may be sent to an aerobic digester such that the
combination of the effluent from the anaerobic and the aerobic digesters
meets the overall quality requirements for recycle in the process.

[0169] In a process utilizing recycle, a purge from the system is
typically required to ensure that components do not build up in the
system over time with repeated recycle. Thus, it would be advantageous to
segregate streams from others that have (i) high concentrations of
inhibitory compounds; and/or (ii) require a higher level of treatment for
recycle in the process than they would for discharge from the process.
These streams could be treated for discharge, for example, in a secondary
aerobic digester, and remain segregated from the other streams, thereby
purging high concentrations of unwanted compounds from the process and
minimizing the overall treatment costs.

[0170] Spent cleaning solutions may be advantageous to segregate for
minimal treatment and discharge from the process as these streams will
likely contain organic compounds as well as inorganic compounds and
suspended solids. However, the composition of such solutions will depend
on the equipment being cleaned and the type of build-up being removed.

[0171] In another example, blowdown streams, which typically result from a
cooling tower or a boiler operation, will generally contain high levels
of inorganic materials and, accordingly, would be most suitably treated
with a reverse osmosis unit or a chemical separation process, such as ion
exchange. It would therefore be advantageous to segregate these streams
and send them only to a reverse osmosis or ion exchange treatment system
for recycle in the process, minimizing the overall treatment system
costs. Feeding this stream to anaerobic or aerobic digesters may not
result in sufficient treatment for recycle in the process.

[0172] By collecting and segregating the streams according to their
treatment requirements, the size of the individual treatment units,
including anaerobic digestion, aerobic digestion, physical separation,
including reverse osmosis, and chemical treatment, including ion
exchange, can be minimized, thereby reducing the overall operating and
capital costs of the treatment area as a whole.

[0173] Examples of treatment processes in which process streams are
segregated according to their treatment requirements are provided in
FIGS. 3A, 3B and 4 described below.

Re-Circulation of Treated Water Streams

[0174] The treated water stream resulting from the treatment process is
re-circulated or recycled into the cellulosic conversion process,
associated utilities, seal water system or a combination thereof. The
terms "re-circulating and recycling" are used interchangeably herein. It
should be understood that more than one treated water stream may be
re-circulated during the step of re-circulating.

[0175] The amount of the treated water stream recycled to the cellulosic
conversion process, associated utilities or the seal water system may be
about 30% to about 99%, or between about 60% and about 95%, or between
about 70% and about 90%, or any range therebetween. It should be
understood that some amount of purge will be required during recycle. The
treated water stream may be fed to a storage tank that is topped up with
fresh water as needed.

[0176] Examples of stages of the process in which the treated water stream
can be re-circulated include, but are not limited to, one or more stages
of the cellulosic conversion process, including: pretreatment, enzymatic
hydrolysis, enzyme fermentation, filtration, ethanol fermentation,
residue processing and a cleaning system, such as a clean in place (CIP)
system

[0177] The treated water stream can also be re-circulated to the
associated utilities or a seal water system.

[0178] By the term "associated utilities", it is meant any equipment used
to support the cellulosic conversion process. This may include a cooling
tower, chiller, fresh water treatment system, fire water system,
compressed air system, chemical storage systems and/or a boiler feed
water system.

[0179] By the term "seal water system", it is meant any system that
supplies water to mechanical seals. For example, seal water may be used
in a flushing operation utilized so as to ensure proper functioning of
the mechanical seal, as discussed above.

Detailed Description of the Preferred Embodiments

[0180] The process of the present invention will be described by reference
to the figures. It should be understood, however, that the figures shown
are merely exemplary of apparatus suitable for carrying out the present
invention and other equivalent means may be utilized without departing
from the spirit of the invention.

[0181] As set forth in FIG. 2, one or more process streams 5 are selected
for treatment by a treatment process comprising at least a step of
anaerobic digestion 10. The process stream 5 fed to anaerobic digestion
comprises one or more streams labeled A, B, C, D, E or F in FIG. 1,
namely spent cleaning solutions, condensate streams, rectifier effluent,
blowdown streams, regenerated streams and spent seal water, respectively.
Subsequent to anaerobic digestion 10, the effluent stream 15 from the
anaerobic digestion 10 is optionally treated in aerobic digestion 20 and
an effluent stream 24 from the aerobic digestion may be subjected to
further physical or chemical separation 30, such as reverse osmosis, ion
exchange or filtration. The treated water 35 resulting from the treatment
process is then recycled to the cellulosic conversion process and/or
related utilities. As noted, such a treatment process requires large
equipment and high operating costs, which negatively impacts the
economics of the process.

[0182] Referring to FIG. 3A, which describes an embodiment of the present
invention, one or more streams 5 are fed to anaerobic digestion 10, while
one or more other streams 8 are fed to aerobic digestion 20. Stream 8
sent to aerobic digestion 20 may include one or more of spent cleaning
solutions, process condensate streams, rectifier effluent and spent seal
water. However, it should be understood that the composition of stream 5
and 8 can vary. For example, both streams may contain process
condensates, possibly containing different types of process condensates
or a fractional amount of the same type of process condensate. An
effluent stream 15 resulting from anaerobic digestion is treated in
aerobic digestion 20 and, optionally, the effluent stream 24 from the
aerobic digestion is subjected to a further physical or chemical
separation 30, such as reverse osmosis, ion exchange or filtration.
Furthermore, an effluent stream 12 from anaerobic digestion 10 may be
sent directly to the optional physical or chemical separation 30. The
treated water resulting from the treatment process is then recycled to
the cellulosic conversion process and/or related utilities.

[0183]FIG. 3B is identical to FIG. 3A except that an additional aerobic
digester 25 is utilized in the configuration. Stream 15 is split into two
streams, one of which is sent to aerobic digester 20 and the other to
aerobic digester 25. Effluent streams 24A and 24B, from the aerobic
digesters 20 and 25, respectively, are fed to the physical or chemical
separation 30. Optionally, the effluent from one of the aerobic digesters
20 or 25 is discharged to the environment.

[0184] Turning now to FIG. 4, one or more streams 5 are fed to anaerobic
digestion 10, while others streams 8 are fed to aerobic digestion 20, and
others 9 to reverse osmosis or ion exchange 13. Streams 9 sent to reverse
osmosis or ion exchange may contain or more of the blowdown, regeneration
or spent seal water streams. The composition of streams 5 and 8 may vary
as required. An effluent stream 15 resulting from anaerobic digestion is
treated in aerobic digestion 20 and the effluent stream 24 from the
aerobic digestion is subjected to reverse osmosis and/or ion exchange 13.
Furthermore, an effluent stream 12 from anaerobic digestion 10 may be
sent directly to the optional physical or chemical separation 30.
Similarly, an effluent stream 7 from anaerobic digestion 20 may be sent
to optional physical or chemical separation 30. The treated water
resulting from the treatment process is then recycled to the cellulosic
conversion process and/or related utilities.